This invention relates to a telecommunications terminal for connection to a network termination of a subscriber and to a telecommunications network comprising a number of telecommunications terminals connected in parallel to a network termination of a subscriber.
EP 98 440 104.2, which has not been published yet, discloses a telecommunications network comprising telecommunications terminals connected in parallel to a single network termination of a subscriber. Although only a single exchange line is present, an external subscriber can selectively call a telecommunications terminal implemented as, e.g., a telephone. Only this telecommunications terminal will then ring. To make this possible, each telecommunications terminal is identified by an identification signal. This identification signal generally forms part of the calling line identification, which is transmitted to the called subscriber terminal after the ringing pulse alerting signal. The telecommunications terminals of the telecommunications network are provided with means for detecting and generating such identification signals. These means generally include a modem which can demodulate the identification signal and passes the demodulated signal on to a processor. After a logic operation, such as a comparison between the demodulated identification signal and the preset, individual identification signal of the telecommunications terminal, it is determined whether the incoming call is destined to this terminal. Only if that is the case will an audible alarm signal be generated in the terminal. Because of the presence of the modem, it is necessary to additionally supply such telecommunications signals with current.
EP 98 440 104.2 deals only with the detection of the individual identification signals. Unlike a digital network termination, such as an ISDN network termination, a transfer of a call existing between an external subscriber and a first telecommunications terminal connected to this analog network termination to a second telecommunications terminal of the telecommunications network is not possible despite the use of individual identification signals. If the external subscriber has dialed the number of the wrong terminal of the telecommunications network by mistake, the call cannot be transferred from that terminal to the desired terminal. Generally, the sole assignment of individual identification signals will not suffice to achieve a performance similar to that obtained with an ISDN network termination, where in addition to the two bearer channels (B channels) for the transmission of user information, a third channel (D channel) is provided for the transmission of control signals.
It is an object of the invention to improve a telecommunications terminal of the above kind and a telecommunications network of the above kind in such a way that the use of several such terminals which are addressable via the same analog network termination becomes more convenient. Another object is to fully utilize the advantages of telecommunications terminals identified by individual identification signals.
These objects are attained by a telecommunications terminal for connection to a network termination of a subscriber, comprising an interface to the subscriber""s in-house power line and addressable via an individual identification signal, wherein the telecommunications terminal further comprises means for generating and detecting control signals which are transferred over the power line to permit the establishment of a call to a further telecommunications terminal connected to the subscriber""s network termination. The objects are further attained by a telecommunications network comprising a number of telecommunications terminals, wherein at least one of the telecommunications terminals comprises means for generating and detecting such control signals.
The use of the subscriber""s in-house power line to transfer control signals between the telecommunications terminals connected in parallel to the network termination makes it possible to establish a call between two telecommunications terminals without having to terminate an existing call with a subscriber external to the network termination. The existing modem for detecting the individual identification signals is additionally used to generate and/or detect the control signals for setting up a call to a further terminal connected to the subscriber""s network termination. The modem itself is controlled by a processor which controls the generation and/or detection of the control signals in accordance with an activatable/deactivatable instruction set.
These instruction sets are advantageously stored in a volatile memory and can be activated by the subscriber if required, for example via a keypad.
With the aid of these control signals, a subscriber at, e.g., one of the telephones connected to the network termination can interrogate a second telephone connected to the network termination for its operating data and, if necessary, change these data. This may be particularly advantageous if two or more telecommunications terminals are connected to the same exchange line. If such terminals are in two different rooms, for example, and one of them includes an answering machine, a subscriber can check from one of the rooms whether a message was recorded on the answering machine in the second room. Besides permitting remote access to answering machine messages, this also makes it possible to adapt some operating data, for example to change a recorded announcement, without having to be in the same room.
Instead of obtaining remote access to an answering machine, a telecommunications terminal serving as a fax machine or a computer (PC) and connected to the network termination can be interrogated for its status and/or the status can be changed.
The transfer of control signals over the in-house power line to establish a call between two telecommunications terminals connected to the same network termination is ideally suited to fully utilizing the advantages of an existing telecommunications network in which all telecommunications terminals are addressable on an individual basis.
Advantageously, a telecommunications terminal as disclosed in EP 98 440 104.2 can be retrofitted with activatable/deactivatable instruction sets for controlling the modem. These instruction sets may be stored centrally in a memory of one of the terminals of the telecommunications network, for example in a nonvolatile memory of a PC. They are then available to all telecommunications terminals via the in-house power line. The instruction sets can be loaded into the PC like a software package, i.e., they can be read from a storage medium via the disk drive of the PC and stored in the nonvolatile memory of the latter.